AWS Certified Solutions Architect Design Cost-Optimized Architectures Syllabus

What is S3 Glacier Deep Archive best for, and what is its retrieval time?

The lowest-cost class for long-term archival (e.g., 7-10 year retention) rarely accessed; standard retrieval takes around 12 hours.

How do S3 Lifecycle policies reduce cost?

They automatically transition objects to cheaper classes after a set number of days and/or expire (delete) old objects and incomplete multipart uploads.

Which EBS volume type is cheapest, and for what workloads?

Cold HDD (sc1) is the lowest cost, for infrequently accessed, throughput-oriented data; st1 (Throughput HDD) suits frequent big sequential workloads like logs/big data.

How can switching from gp2 to gp3 EBS save money?

gp3 is ~20% cheaper per GB than gp2 and lets you provision IOPS and throughput independently of size, so you don't overpay on capacity just to get performance.

What hidden storage cost grows over time with EBS, and how do you control it?

EBS snapshots accumulate in S3; use Data Lifecycle Manager (DLM) to automate snapshot creation, retention, and deletion of stale snapshots.

What is the general rule about AWS data transfer pricing direction?

Inbound data transfer to AWS is generally free; outbound (egress) to the internet is charged, and cross-region/cross-AZ transfer incurs costs.

How does a VPC endpoint reduce data transfer cost?

It keeps traffic to AWS services (e.g., S3, DynamoDB via Gateway endpoints) on the AWS private network, avoiding NAT Gateway processing/data charges and internet egress.

How does CloudFront help lower data transfer costs?

Caching at edge locations reduces origin fetches, and CloudFront egress rates to the internet are lower than direct EC2/S3 egress (plus free transfer from S3/EC2 origins to CloudFront).

What is a common costly mistake with NAT Gateways?

Routing high-volume traffic (including to AWS services) through a NAT Gateway incurs hourly + per-GB processing charges; use VPC/Gateway endpoints or place resources appropriately to avoid it.

Is data transfer between EC2 instances in the same AZ using private IPs free?

Yes — same-AZ traffic over private IPv4 addresses is free; using public IPs or crossing AZs/regions incurs charges.

Which RDS/Aurora purchasing option reduces database cost for steady workloads?

Reserved DB Instances — 1 or 3 year commitments giving large discounts over On-Demand for predictable, always-on databases.

How does Aurora Serverless v2 optimize database cost?

It auto-scales capacity in fine-grained ACU increments to match load and scales down during low usage, so you pay only for the capacity actually consumed.

For variable/unpredictable DynamoDB traffic, which capacity mode is most cost-effective?

On-Demand capacity mode — pay per request with no capacity planning; use Provisioned (with Auto Scaling/reserved capacity) for steady, predictable traffic to save more.

How can read replicas or caching reduce database cost?

Offloading reads to replicas or an in-memory cache (ElastiCache/DAX) lets you use a smaller primary instance and avoid scaling up the expensive write tier.

What DynamoDB feature automatically removes stale items to save storage cost?

Time to Live (TTL) — it deletes expired items automatically at no extra cost, reducing stored data and table size.

What does AWS Budgets do?

Lets you set custom cost/usage (or RI/SP utilization/coverage) thresholds and triggers alerts or automated actions when actual or forecasted spend exceeds them.

What is the difference between Cost Explorer and AWS Cost and Usage Report (CUR)?

Cost Explorer gives interactive visualization/forecasting; the CUR is the most detailed line-item dataset (delivered to S3, queryable via Athena/QuickSight) for deep analysis.

What is AWS Budgets Actions used for?

To automatically respond when a budget is breached — e.g., apply an IAM/SCP policy, stop EC2/RDS instances, or send approvals — to enforce cost controls.

What does AWS Cost Anomaly Detection do?

Uses ML to monitor spend and automatically alert you to unusual cost spikes by service, account, or category, with root-cause analysis.

Which free AWS tool reviews your account for cost optimization (and other pillars)?

AWS Trusted Advisor — its cost optimization checks flag idle/underutilized resources, unassociated EIPs, idle load balancers, and RI opportunities.

What is the AWS Pricing Calculator used for?

Estimating the cost of an architecture before deployment by modeling services, usage, and pricing options to compare design choices.

What kinds of resources does Trusted Advisor flag as idle/wasted spend?

Low-utilization EC2 instances, idle load balancers and RDS, unattached EBS volumes, unassociated Elastic IPs, and under-provisioned RIs/Savings Plans.

What is 'right-sizing' and why is it the first cost-optimization step?

Matching instance/resource size to actual workload demand (using metrics) to eliminate over-provisioning — typically the largest, lowest-risk savings before buying commitments.

What does the Savings Plans recommendation in Cost Explorer provide?

It analyzes past usage to recommend a commitment level (hourly $) and term that maximizes savings without over-committing.

Why purchase commitments (RIs/Savings Plans) only after right-sizing?

Committing to oversized resources locks in waste for 1-3 years; right-size first, then buy commitments on the optimized baseline.

How does Auto Scaling contribute to cost optimization?

It adds capacity only when demand requires and removes it when idle (scheduled or dynamic), so you don't pay for over-provisioned steady-state capacity.

How do AWS Organizations enable consolidated cost benefits?

Consolidated billing aggregates usage across accounts to share volume discounts and RI/Savings Plan benefits, with one bill and per-account cost visibility.

What are Service Control Policies (SCPs) and how do they aid cost control?

Org-level guardrails that restrict which services/regions/instance types accounts can use, preventing costly or non-compliant resource creation.

What is AWS Control Tower's role in cost governance?

It sets up a multi-account landing zone with guardrails and centralized policies, helping enforce consistent cost and security controls across the organization.

How do cost categories help large organizations?

They group costs into custom business dimensions (team, product, cost center) using rules, enabling chargeback/showback and clearer reporting across many accounts.

What is the benefit of a multi-account strategy for cost management?

Separating workloads/teams/environments into accounts gives clear cost isolation, easier budgets and tagging enforcement, and blast-radius and governance boundaries.